1930’s Europe was politically polarised – Stalin’s communist Russia opposed by the fascist regimes of Hitler’s Germany & Mussolini’s Italy. In the middle sat Great Britain, France and the rest of Europe, all trying to avoid conflict.
The British, still coming to terms with the horrors of the 1914-18 war played a game of appeasement. The ‘establishment’ saw many aspects of fascism in a favourable light and of course Germany was acting as a block against the advance of communism. Britain’s ruling class had an almost numbing fear of Stalin & the Bolsheviks. Moseley’s fascist black shirts were vicious thugs but at least he was from the right class. Unfortunately this attitude to Stalin was misplaced, it allowed Hitler and Mussolini to cleverly further their expansionist plans and at the same time proclaim their friendship to fellow western countries all fending off the threat of the’ red terror’.So when Franco launched his rebellion in 1936 it created awkward problems for the rest of Europe. I think it’s fair to say certainly Hitler and the British Government (elements of it at least) knew of Franco’s proposed uprising. Many of the landed classes in Western Europe were disturbed by the idea that wealth – especially agricultural land – was being redistributed amongst the landless peasants. So privately they saw Franco putting a welcome stop to this kind of social reform. The’ landed gentry’ preferred to return to the Status Quo of pre 1930 feudal Spain and to halt in the tracks any similar anarchist sentiments in their own countries.
Franco’s uprising started in Britain (the aircraft for the Canary Island airlift coming from Croydon airport) and got underway with the help – probably unofficial - of Royal Navy communications in Gibraltar.
Then horror upon horror nothing went to plan – the Spanish Navy largely stayed loyal to the Government – minus most of its officers and so it looked as though Franco’s troops would be stuck in North Africa unable to cross the straits of Gibraltar.

However Hitler & Mussolini swiftly came to the rescue and provided aircraft to lift the troops to the mainland whilst German battleships patrolled the Mediterranean.
The governments of Europe stood back and gasped – this wasn’t meant to happen. Not really wanting a ‘red’ country in southern Europe was one thing but another fascist aided state was quite another. Hitler & Mussolini saw a great opportunity to gain a foothold in Spain, they supplied planes, equipment and troops - a victorious Franco would be an important ally.

Stalin meanwhile found himself wrong footed. Although he didn’t like the Popular Front government it was at least was left wing. Never happy with the liberal influence he was already secretly infiltrating Bolsheviks into key positions in Spain. Now the situation was more urgent requiring immediate action, he offered financial & military support and planned to continue steering Spanish politics in the direction of his liking.
See Condor Legion